This is how I do it with file_sink: boost::iostreams::filtering_ostream output_file; output_file.push(boost::iostreams::bzip2_compressor(boost::iostreams::bzip2_params(9))); output_file.push(boost::iostreams::file_sink("file.bz2", std::ios_base::binary)); output_file<<"blalba"; I think if you do just this, nothing happen until output_file is destroyed. So enclose in { }. Frédéric

On 26/07/2013 14:49, Larry Evans wrote:

On 07/26/13 06:39, Frédéric Bron wrote:

...

This is how I do it with file_sink:

boost::iostreams::filtering_ostream output_file; output_file.push(boost::iostreams::bzip2_compressor(boost::iostreams::bzip2_params(9))); output_file.push(boost::iostreams::file_sink("file.bz2", std::ios_base::binary)); output_file<<"blalba";

I think if you do just this, nothing happen until output_file is destroyed. So enclose in { }.

Frédéric

Thanks Frederic.

However, I think this is not obvious. I would have thought Ken's solution would have worked. I would have also thought mine would have worked until I saw Ken's which indicated std::ios_base::binary was needed when the std::ofstream was created.

Is there anywhere in the docs explaining why your method works and Ken's doesn't?

-regards, Larry

Larry, Passing the filtering_streambuf to a stream constructor should indeed work, as you expect. The test program below works fine for me - boost 1_49 on mingw 4.4. Ken Appleby Soft Optics Ltd ------------------- #include <iostream> #include <fstream> #include #include #include int main() { try { { std::ofstream myFile("hello.gz", std::ios_base::out | std::ios_base::binary); boost::iostreams::filtering_streambufboost::iostreams::output out; out.push(boost::iostreams::gzip_compressor()); out.push( myFile ); std::ostream os(&out); os << "text I want to be compressed and end up in the file..."; } { std::ifstream myFile( "hello.gz", std::ios::in | std::ios::binary ); boost::iostreams::filtering_streambuf< boost::iostreams::input > in; in.push( boost::iostreams::gzip_decompressor() ); in.push( myFile ); std::istream is( &in ); std::string text; while ( is.good() ) { char ch = is.get(); if ( is.good() ) text.push_back( ch ); } std::cout << "text from file is \"" << text << "\"" << std::endl << std::flush; } } catch ( std::exception& e ) { std::cerr << e.what() << std::endl; } }

On 07/26/13 21:26, Stephen Greenfield wrote: [snip]

3) Holger Gerth questioned why I was using filtering_streambuf when I could've been using filtering_stream. Truth is, I wasn't sure, however, in my experiments I could neither construct the ostream (which I required to pass to other functions) from the filtering_stream, nor could I pass the filtering_stream in place of the ostream I required.

Even after reading several articles on filtering_streambuf vs filtering_stream, I'm still mystified how and why (FOR MY PURPOSE) I would use the filtering_stream over constructing an ostream from a filtering_streambuf.

[snip] Hi Stephen, I thought the filtering_stream would be derived from std::ostream, at least according to: Derived class of std::basic_istream, std::basic_ostream or std::basic_iostream, used to perform filtering. quoted from: http://www.boost.org/doc/libs/1_54_0/libs/iostreams/doc/classes/filtering_st... Did you not find this so, or do you needs require something more specific than std::ostream& to be passed to the other functions you mention? -regards, Larry

On 07/28/13 23:28, Stephen Greenfield wrote:

On 7/28/13 8:45 PM, "Larry Evans" mailto:cppljevans@suddenlink.net> wrote:

I thought the filtering_stream would be derived from std::ostream, at least according to:

Derived class of std::basic_istream, std::basic_ostream or std::basic_iostream, used to perform filtering.

quoted from:

http://www.boost.org/doc/libs/1_54_0/libs/iostreams/doc/classes/filtering_st...

Did you not find this so, or do you needs require something more specific than std::ostream& to be passed to the other functions you mention?

Larry --

Thanks! You would've thought that — and you know what? You would be CORRECT.

I thought I had tested every possible case — but I think I did that BEFORE discovering my error with closing the file before destructing the filtering_streambuf/filtering_ostream.

You (and everyone else) were ABSOLUTELY CORRECT. When I changed my code from a filtering_streambuf:

ofstream myXMLFile (destPath, std::ios_base::out | std::ios_base::app | std::ios_base::binary); boost::iostreams::filtering_streambufboost::iostreams::output filteringOStream; filteringOStream.push(boost::iostreams::zlib_compressor()); filteringOStream.push(myXMLFile); std::ostream myExportedXMLFilteringOStream(&filteringOStream); Foo(myExportedXMLFilteringOStream);

TO A filtering_ostream:

ofstream myXMLFile (destPath, std::ios_base::out | std::ios_base::app | std::ios_base::binary); boost::iostreams::filtering_ostream myExportedXMLFilteringOStream; myExportedXMLFilteringOStream.push(boost::iostreams::zlib_compressor()); myExportedXMLFilteringOStream.push(myXMLFile); Foo(myExportedXMLFilteringOStream);

Thank you so much for tying up that loose end! I'm assuming the filtering_ostream is of course more efficient than the filtering_streambuf scenario? I don't know, but I guess so.

BTW, I tried modifying Ken's code to use filtering_ostream instead of filtering_streambuf, and it worked. I also removed the ios_base flags and it still worked. Then I tried using stringstream instead of filestream and it no longer worked. Anyone have any clues about why stringstream doesn't work? The code is attached. With the attached code and attached Jamfile.v2, and with: #define USE_STRINGSTRM in the code, the KenApplebyStrm.output produced by bjam is in the next attachment. In contrast, with: //#define USE_STRINGSTRM int the code, the KenApplebyStrm.output produced by bjam is in the last attachment.

Best Regards,

Stephen

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On 07/29/13 11:27, Larry Evans wrote:

On 07/29/13 11:10, Larry Evans wrote: [snip]

...

BTW, I tried modifying Ken's code to use filtering_ostream instead of filtering_streambuf, and it worked. I also removed the ios_base flags and it still worked. Then I tried using stringstream instead of filestream and it no longer worked. Anyone have any clues about why stringstream doesn't work? The code is attached. With the attached code and attached Jamfile.v2, and with:

#define USE_STRINGSTRM

in the code, the KenApplebyStrm.output produced by bjam is in the next attachment. In contrast, with: //#define USE_STRINGSTRM int the code, the KenApplebyStrm.output produced by bjam is in the last attachment. [snip] OOPS. The code attached previously used streambuf instead of stream. The current attachment uses stream.

Based on running the attached both with: #define USE_FILT_COMPRESS then with: //#define USE_FILT_COMPRESS on line 40 showed that using the gzip_decompressor starts reading at the end of the stream instead of at the beginning. The corresponding outputs are also attached. This contrasts with the count filter which starts reading, as one would expect, at the beginning of the stream. Still trying to track down why. -Larry

On 07/31/13 07:16, Larry Evans wrote:

On 07/30/13 13:59, Larry Evans wrote:

...

On 07/29/13 11:27, Larry Evans wrote:

...

On 07/29/13 11:10, Larry Evans wrote: [snip]

...

BTW, I tried modifying Ken's code to use filtering_ostream instead of filtering_streambuf, and it worked. I also removed the ios_base flags and it still worked. Then I tried using stringstream instead of filestream and it no longer worked. Anyone have any clues about why stringstream doesn't work? The code is attached. With the attached code and attached Jamfile.v2, and with:

#define USE_STRINGSTRM

in the code, the KenApplebyStrm.output produced by bjam is in the next attachment. In contrast, with: //#define USE_STRINGSTRM int the code, the KenApplebyStrm.output produced by bjam is in the last attachment. [snip] OOPS. The code attached previously used streambuf instead of stream. The current attachment uses stream.

Based on running the attached both with:

#define USE_FILT_COMPRESS

then with:

//#define USE_FILT_COMPRESS

on line 40 showed that using the gzip_decompressor starts reading at the end of the stream instead of at the beginning.

The corresponding outputs are also attached.

This contrasts with the count filter which starts reading, as one would expect, at the beginning of the stream.

Still trying to track down why.

Changing the:

out.flush()

around line 93 to:

out.strict_sync();

which is described here:

http://www.boost.org/doc/libs/1_54_0/libs/iostreams/doc/classes/filtering_st...

failed to solve problem :( Still trying to track down why.

Maybe the reason is the filter's are not flushable. However, even though the counter filter is also not flushable, the output turns out OK. Finally, I read about reset and pop: http://www.boost.org/doc/libs/1_54_0/libs/iostreams/doc/classes/filtering_st... and both worked to get proper value for actual_out in the attached. The root cause of my difficulties was my assumptions about what out.flush() or out.strict_sync() should have done, and not reading about reset or pop. However, my excuse was that flush and sync are names with pretty much standard meanings; yet, with iostreams, those meanings don't apply completely :(. Hopefully this will help others running into the same problem. -regards, Larry